Thermally resistant fabric sheets for use as single or outer layer of protective garments are known in the art.
WO 00/66823 discloses a fire resistant material made of woven meta-aramid and polyamideimide fibers strengthened by an interwoven mesh of para-aramid fibers or polyparaphenylene terephthalamide, and fire resistant clothing made of this material.
WO 02/079555 discloses a reinforced fabric especially for thermal protection clothing, the fabric being reinforced by interlaced warp yarn weaves and weft yarn weaves of high-strength materials.
WO 02/20887 discloses a fire resistant material comprising a woven faced fabric composed of meta-aramid fibers, polyamideimide fibers and mixtures thereof, and a woven back fabric of low shrinkage fibers selected from para-aramid, polyparaphenylene terephthalamide copolymer and their mixtures. The two layers could be interwoven together at points forming a sort of grid.
WO 03/039280 describes a sheet of complex or multilayer structure especially intended for a thermal barrier in protective clothing for fire fighters, where the layers of material are interwoven to form pockets. The outer layer shrinks under the effect of heat to form pockets underneath, the pockets forming tubes along the inside face. FIGS. 5 and 7 of this prior art document illustrate the pockets and the interweaving pattern, respectively. WO 03/039281 describes a sheet of complex or multilayer structure for thermal barriers in fire fighters' protective clothing, where the layers of material are interwoven such that when the outer layer shrinks under the effect of heat the connecting fibers straighten to increase the space between the layers.
WO 2004/023909 (corresponding to EP 1 542 558), the content of which is incorporated by reference in its entirety in the present application, discloses a fabric for protective garments that is heat, flame and electric arc resistant. The fabric for use as single or outer layer of protective garments, comprises at least two separate single plies each having a warp and a weft system, the at least two separate single plies being assembled together at predefined positions so as to build pockets, the warp and the weft systems of the at least two separate single plies being based on materials independently chosen from the group consisting of aramid fibers and filaments, polybenzimidazol fibers and filaments, polyamidimid fibers and filaments, poly (paraphephenylene benzobisaxazole) fibers and filaments, phenol-formaldehyde fibers and filaments, melamine fibers and filaments, natural fibers and filaments, synthetic fibers and filaments, artificial fibers and filaments, glass fibers and filaments, carbon fibers and filaments, metal fibers and filaments, and composites thereof.
Due to its peculiar structure, this fabric may have a specific weight which is considerably lower than that of known fabrics having comparable mechanical and thermal properties.
Another aspect of WO 2004/023909 is a garment for protection against heat, flames and electric arc comprising the above fabric as single or outer layer.
The garment according to WO 2004/023909 strongly improves the wearer's comfort both during normal and critical situations. It is lighter and thinner than conventional garments having similar mechanical and thermal properties and it enables a higher heat and vapour dissipation from the wearer surface to the environment.
WO 2006/026538 (corresponding to EP 1 796 492), the content of which is incorporated by reference in its entirety in the present application discloses a thermally resistant composite fabric sheet wherein the array of connecting lines is constituted by a plurality of isolated single connecting lines and/or by a plurality of isolated groups of connecting lines. The connecting lines are arranged at different angles and are spaced apart from one another to leave, between the isolated single connecting lines and/or between the isolated groups of connecting lines, gaps where the two layers are not connected to one another. These gaps unite a continuous expanse of the two unconnected layers that surrounds each isolated connecting line and/or each isolated group of connecting lines. This continuous expanse of the unconnected fabric layers has a labyrinth-like structure delimited by the connecting lines at different angles such that, when a given area of the outside layer is subjected to intense heat resulting in thermal shrinkage, the inside layer forms under the given area a series of self-closing bubble-like pockets that form individually in discrete areas of the continuous expanse between the connecting lines and that are inhibited by the labyrinth-like structure from propagating along or across the sheet outside said given area.
The connecting lines or groups of connecting lines are isolated and surrounded like islands in the expanses of unconnected fabric layers, with the connecting lines at angles forming a sort of labyrinth that prevents the bubbles from forming tubes. The connecting lines are conveniently arranged in a geometrically repeating pattern with the continuous expanse forming wavy paths that meander around the pattern of lines. The connecting lines can for example be arranged in a plurality of groups each composed of a plurality of connecting lines arranged for instance in a generally Y, V, L, T, H, X or Z configuration with the lines extending from at least one convergence point, the lines being connected together at, or being spaced apart from, their convergence point(s).
The special structure of the thermally-resistant composite fabric sheet according to WO 2006/026538 provides an improved combination of properties over prior art structures, in particular a combination of high thermal performance with improved physical characteristics after the fabrics have been exposed to heat, which leads to enhanced wearer comfort due to the fact that these performances can be achieved with fabrics of lower weight. Therefore, garments of the same thermal performance can be made with lighter fabrics, making the garments more comfortable to wear.
When the outer face of the fabric according to the invention is, for example, exposed to a flame or another intense source of heat, the outside fabric layer is caused to shrink. The inside layer is shielded from the heat source and does not shrink, or shrinks much less. Shrinkage of the outside fabric layer is constrained by the connecting lines that are isolated in a pattern, surrounded by the unconnected layers. The bubble-like pockets that form are localized under the heated area; the limited propagation of these self-closing pockets means that the thus-formed insulating space is effective to protect the underlying area. Thus, heat is not unwantedly transmitted to adjacent areas by the formation of tubes. This formation of bubble-like air spaces under the area that is exposed to intense heat provides the high thermal performance of the fabric.
After exposure to intense heat, the fabric also has improved physical characteristics, namely a good tear resistance and tensile strength. When the heated outside layer shrinks, it acts as a heat absorber, sacrificing some of its physical strength, while the inside layer remains intact. Furthermore, the connecting lines uniting the two fabric layers also sacrifice some physical strength leading to a weakness of the fabric along such lines where the fabric can tear. However, due to the peculiar discontinuity in the connecting lines and the resulting unconnected expanses of the fabric according to the present invention, such tears cannot propagate to other zones which have not been exposed to heat and which are therefore undamaged. As a result, the outer layer of the fabric sheet demonstrates good tear resistance and tensile strength after exposure to intense heat, the inside layer remaining protected and the intact unconnected expanse of the inside layer retaining its strength. This could be extremely important for firemen's clothing where, for example, a fireman in a burning structure has to be pulled by his clothing to remove him from a critical situation.
Despite these proposals, there remains a need for thermally-resistant fabrics that combine wearer comfort, high thermal performance, high resistance to abrasion, high durability, improved mechanical performances and electrical arc protection.